1. Field of the Invention
The present invention is directed to solenoid actuators. More particularly, the present invention is directed to a two-stage solenoid valve for selectively providing a first and a second flow rate therethrough.
2. Description of the Prior Art
Prior attempts to provide two different flow rates have included the use of two valves in parallel flow lines with a selective actuation of the valves which may have had different size flow control orifices. Another prior art solution to the problem used a single orifice valve with a single coil and armature and a half-wave rectified alternating current (AC) input energizing signal. The energizing signal produced an oscillation of the armature at a fixed frequency to produce a reduced flow rate relative to a non-oscillatory fully open position of the armature produced by a non-rectified energizing signal. These prior art approaches have inherent disadvantages such as chatter at reduced flow in the case of the oscillating armature and increased cost of the extra valve and plumbing in the case of the dual valve. Accordingly, in order to overcome the aforesaid shortcomings of the prior art, it is desirable to provide a valve having a selectively variable flow rate while exhibiting a quiet operation and direct operation on alternating current (AC) and direct current (DC).